Question for you electricians RE: PID for a 220 volt oven

[scotner]

There are several threads on how to build a PID to control 110 volt devices. My question is about using a PID to control a wall oven. I pulled the sheet metal off to explore the control board and wiring for my oven. If I traced it out correctly it appears that one side of the 220 is connected directly to both heating elements. There are two relays on the board, one marked bake and the other is marked broil. The other side of the 220 connects to them. So you just need to break one side to cycle the heat, right? Just disconnect from the control board and use my SSR to replace the bake relay. Then pick up one side of the 220 and the neutral to get 110 for the PID?

I have wired several 220 devices but never really looked at how they control. I found one schematic online showing two SSRs used to break both sides of the wiring to the element. Mine does not appear to be wired that way and I do not see why that would be necessayry. Never too old to learn. Thanks.

[rancher1913]

most 220 heaters only break one leg to control temp. your pid basicly replaces the existing thermostat. most ovens dont need a electronic pid the existing tstat is usually fine, just need to calibrate it. pm hatch, he has probably forgot more about pids then most of us know.

[Paper Puncher]

With 220v both sides are hot in relation to ground. So even with one side open the coil/heating element is still hot (120v). That is the reason (safety) that you see a relay on both sides of the heating coil.

[scotner]

I can calibrate the offset to where the temperature matches the set point. I'm trying to eliminate variation in the temperature. That's the purpose for the PID in this case.

I can add a second relay to break both sides of it but as it's currently set up it does appear to only break one side. Is that correct? So you're saying I need to modify the way it's originally set up. That's not a problem if that's what needs to be done. I'll just have to order a second relay.

[jsizemore]

I would wire with 2 SSR. I've seen too many bake elements blown in two. With 120V still going to part of element, it could be an accident waiting to happen. Sometimes folks don't do what's best and unplug or kill the breaker.

[scotner]

OK. Thanks. I will go that route. Thanks for the replies.